1. Field of the Invention
This invention relates to fuel-injected gasoline engines and, in particular, to improved fuel routing systems for such engines.
2. Description of the Prior Art
In a fuel-injected gasoline engine, gasoline is supplied at a relatively high pressure to one or more injectors which are connected directly to the engine cylinders or to an intake manifold leading to the cylinders. A common configuration for delivering fuel to such engines uses two pumps: a low pressure pump either near or in the vehicle's gas tank and a high pressure pump connected to the injectors. For vehicles having two gas tanks, e.g., medium duty and larger trucks, off-road vehicles, and the like, an additional low pressure pump is used for the second tank.
For single tank systems employing the above configuration, two lines run between the gas tank and the injectors: a feed line which includes the low pressure pump, the high pressure pump, and at least one fuel filter, normally located between the low and high pressure pumps; and a return line which carries non-injected fuel back to the gas tank. Two tank systems include a feed and a return line for each tank and a selector valve for selecting the tank which is to supply fuel and receive non-injected fuel. The selector valve is usually placed before the fuel filter, so that one filter can serve both tanks.
A typical selector valve 10 of the type used in the prior art is shown in FIG. 12. As shown therein, reversible electric motor 12 is connected to valve assembly 14 by screw drive 8 so that rotation of the motor in one direction causes engine feed and return lines 16 and 18 to be connected to feed and return lines 20 and 22 from tank 1, while rotation of the motor in the other direction connects the engine feed and return lines to feed and return lines 24 and 26 from tank 2. Electrical control of motor 12 is provided by means of a wiring harness (not shown) which is connected to selector valve 10 by male spade lugs 28 and by means of electrical contacts 30 and 32 which move with the screw drive and make contact with electrical contacts 34 and 36 carried by the selector valve housing.
Prior art fuel delivery systems of the above type have suffered a number of disadvantages. For example, vehicles equipped with such systems have exhibited fuel starvation problems when traveling over rough terrain, and, in particular, when traveling over steep inclines, even with as much as an eighth of a tank of gas left in the vehicle. This starvation problem is caused by a lack of fuel at the inlet to the low pressure pump due to sloshing of the fuel mass as a function of vehicle attitude and dynamics.
Various approaches have been considered for solving this fuel starvation problem. For example, it is possible to redesign the vehicle's gas tank so as to increase the probability that fuel will be present at the inlet to the low pressure pump. Such a redesign, however, can be very expensive, especially for a vehicle which is already in production. Also, due to design constraints imposed by safety, appearance and other considerations, for certain vehicles, fuel tank redesign will not completely solve the fuel starvation problem.
Alternatively, the fuel starvation problem can theoretically be eliminated by placing a reserve fuel mass between the low pressure pump and the high pressure pump so that the high pressure pump can continue to operate even though the low pressure pump is not receiving fuel from the gas tank. Unfortunately, in practice, this approach turns out to be unworkable. This is so because the high pressure pump supplies both the fuel injected into the vehicle's engine and the fuel returned to the vehicle's gas tank. Accordingly, to be able to supply the high pressure pump with fuel for periods of up to 5 minutes and longer, the reserve fuel mass would have to have a volume beyond that which can conveniently be incorporated into a standard truck or automobile.
Besides the fuel starvation problem, fuel-injected engines using the above type of fuel delivery system have also suffered from problems caused by air entrainment in the fuel stream fed to the injectors. Such entrainment is particularly severe after an episode of fuel starvation during which large amounts of air are introduced into the fuel delivery system through the low pressure pump. Such air entrainment results in loss of engine power and has been found to be one of the primary sources of rough engine idling.
In addition to the above problems which have plagued both one tank and two tank systems, the two tank systems, and, in particular, the selector valves used with those systems, have had their own special problems. Specifically, the use of an electric motor to actuate the valve has resulted in a complex, expensive, and delicate device.
As illustrated in FIG. 12, the prior art selector valves have required a multi-component drive train, composed of more than a dozen, intricate moving parts, to connect the electric motor to the valves. In addition, to actuate and control the motor has required even more parts, including complex and delicate electrical switching contacts as part of the valve itself and an electrical harness to connect the valve to the vehicle's main electrical system. Moreover, due to size and cost limitations, only small electric motors have been used in the prior art valves, and thus only small valve actuation forces have been achieved by these devices.
Plainly, in terms of ease of assembly, quality control testing, cost, and the overall effectiveness of the device, the prior art selector valves have been far from ideal.